How to Calculate Relative Risk

Calculating relative risk (RR) also known as the risk ratio, according to STATS, "is a comparison between different risk levels." It is used to understand the risk of an incident relative to exposure. Relative risk does not tell you anything about the actual risk, the chance of the risk occurring. The Journal of American Medicine defines relative risk as "a method of correcting the odds ratio in cohort studies of common outcomes." Relative risk is commonly used in the health care industry to calculate the risk of a specific population in comparison to the entire population.

Things You'll Need

• Relative risk formula
• Absolute risk of comparables

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Instructions

• 1

  Define the relative risk formula. Relative risk is the absolute risk of a specific group divided by the absolute risk of all other groups.

• 2

  Calculate the absolute risk of the two comparables. For instance, 50 out of every 1,000 green apples spoil when shipped, compared to 32 of every 1,000 of all other types of apples spoil when shipped. Which means, the absolute risk for green apples is 50/1,000, or 0.05, and the absolute risk for all other types of apples is 30 divided by 1,000, or 0.03.

• 3

  Using the relative risk formula, you plug in the absolute values calculated. So in the above example, green apples were our specific group and the absolute value of green apples was 0.05, so divide this by the absolute value for all other apples which equaled 0.03, or (0.05/0.03) = 1.66. Therefore we can say, green apples are 1.7 times as likely to bruise when shipped compared to all other apples.